Tuesday, January 17, 2017

Minority opinion on classification of Ponderosa Pine

The recent study of Willyard et al (2017) on lineages of Ponderosa Pine (Pinus ponderosa) is important and at the same time highly problematic.  The study strongly demonstrates that Pinus ponderosa is a complex lineage containing several distinct taxa which merit taxonomic treatment. 
Willyard et al (2017) suggest treatment of the taxa in the lineage as full species:  Pinus ponderosa, P. benthamiana, P. scophulorum and P. brachyptera.   

This will not find wide acceptance in the non-botanical world of commerce.  A long history of practical use, common understanding, and governmental inertia will result in default back to a broadly circumscribed, single species model.  Unfortunately, the single taxon model fails to account for geographic and evolutionary distinct units within this clade, and is not a scientifically supported, proper classification.  Put crudely, the guy at the lumber yard is not going to care...!

The principal purpose of any classification is utility.  Treatment of the taxa of the Pinus ponderosa lineage as subspecies would have a much higher probability of gaining wide application.   Without reference to geography, the identification of individual trees is not easy, even with mature cones and bud-color features at hand, because the overall morphogical similarity between the individual taxa is substantial (Callaham 2013).  Users of a classification which employs infrataxa can refer only to Pinus ponderosa generally in instances where their determination of subspecies is unimportant (i.e. this timber is ponderosa pine) or in geographic areas where the taxa overlap (i.e. in the KR-CaRH region of California, where both P. ponderosa and P. benthamiana haplotypes are present). 

The five validly published taxa treated as subspecies are:
Pinus ponderosa P. Lawson & C. Lawson ssp. ponderosa, Agric. Man. 354 (-355). 1836
P. ponderosa ssp. ssp. benthamiana (Hartw.) Silba -- J. Int. Conifer Preserv. Soc. 16(1): 30. 2009
P. ponderosa ssp. brachyptera (Engelm.) Silba -- J. Int. Conifer Preserv. Soc. 18(1): 16. 2011
P. ponderosa ssp. scopulorum (Engelm.) A. E. Murray -- Kalmia 12: 23. 1982
P. ponderosa ssp. washoensis (H. Mason & Stockw.) A. E. Murray, Kalmia 12: 23. 1982.

The treatment of the taxa of Pinus ponderosa as subspecies is consistent with broad practice for many higher plants.  Treatment of the clade as varieties (where not all of the required names are valid) is not consistent with treatment models which have survived the test of time (Simpson 1945, Clausen 1951 Dobzhansky 1951, Stebbins 1966, Mayr 1982) and is inconsistent with common practice in the larger portions as applied to higher plants (Briggs & Walters 1971) worldwide.

In plant taxonomy, my opinion is that we devalue the worth of our effort when we do not defer to the practical needs of society at large whom consume our names.  

The five ponderosa pines are subspecies.

Briggs, D., & S. M. Walters.  1971    Plant Variation and Evolution.   White & Gilbert, U.K.
Callaham , R. Z. 2013 . Pinus ponderosa : Geographic races and subspecies based on morphological variation. USDA Forest Service, Pacific Southwest Research Station PSW-RP-265. Washington, D.C.
Clausen J.  1961.  Stages in the evolution of plant species.  Cornell Univ. Press, Ithaca, N.Y.
Dobzhansky, T.  1951.  Genetics and the origin of species.  Columbia Univ. Press, New York, N.Y.
Mayr, E.  1982.  Growth of Biological Thought: Diversity, Evolution, and Inheritance. Harvard Univ. Press Cambridge, M.A.
Simpson, G. G. 1945. The Principles of Classification and a Classification of Mammals. Bull. American Museum Nat. Hist. 85: 1-23.
Stebbins, G. L. 1966.  Processes of organic evolution.  Prentice Hall, Engelwood Cliffs, N.J.
Willyard, A. W. et al. 2017.  Pinus ponderosa: A checkered past obscured four species.  Amer. J. Bot. 104(1):1-21.